Inflatable support appliances use inflatable cushions or air bags as the supporting surface for a patient. By using a fluid support medium such as air within the bags, an irregularly shaped body placed on top of the air bags will deform the supporting surface in such a manner so as to provide a more uniform distribution of load bearing pressure points than can be attained with a conventional mattress. When a patient lies supinely on a flat surface, or even on a conventional mattress, most of the load is born by protuberances of the posterior surface of the body such as the heels, the buttocks, the scapulae, and the occipital region of the head. The relatively small areas of soft tissue at these points are then subjected to high pressures by being compressed between the skeleton and the supporting surface. When this pressure becomes great enough to cause collapse of small capillaries and veins, pressure sores may result. Inflatable support appliances, by uniformly distributing the supporting pressure points along the body surface, reduce the pressure at these critical areas.
One species of inflatable support appliances, called low air loss beds, utilizes a continuous flow of air through the bags from a source of pressurized air (or other gas) such as a blower, the air being exhausted through separate outlets or pores in the fabric of the bags. One of the first such beds is described in U.S. Pat. No. 3,822,425 issued to Scales, the disclosure of which is hereby incorporatd by reference. Low air loss beds are particularly advantageous when the patient support surface of the bags is made from a fabric permeable to water vapor such as GORE-TEX fabric. Patients are predisposed to pressure sores by the accumulation of moisture at the skin surface. By maintaining a low water vapor concentration within the bags with a continuous flow of air, accumulated moisture can diffuse from the patient's skin across the fabric of the patient support surface.
One problem associated with inflatable support appliances, however, comes about when it is desired to cool the patient support surface. These occasions may arise in treating burn patients as well as other types of febrile patients. It may also be desired to heat the patient support surface. In either case, the usual method is to interpose a cooling (or heating) pad between the patient and the support surface. The obvious disadvantage with this practice, however, is that it compromises the uniform supporting characteristics of the inflatable cushions. Furthermore, in the case of low air loss beds, the moisture removing function is also compromised.
With low air loss beds, which use a continuous flow of air, an alternative solution would seem to be to cool the air as it exits from the blower. Due to the large volume of air circulated over a period of time, however, this method is prohibitively expensive. Furthermore, any cooling unit which cooled that large a volume of air would necessarily raise the ambient temperature of the room to uncomfortable levels.
There have been attempts in the past to provide inflatable cushions or mattresses containing tubing through which a heating or cooling medium is circulated. U.S. Pat. No. 800,967 discloses one such device. In this device, however, the tubing carrying the cooling or heating medium is mounted near the bottom of the mattress so that the tubing does not touch the supporting surface of the mattress. Therefore, heat transfer between the supporting surface and the cooling or heating medium must occur through the interposed air within the mattress. This necessarily limits the efficiency of the heat transfer process since air is a very poor heat conductor. Another disadvantage with arrangements of this type is that it is difficult to remove the tubing, if it can be removed at all, in order to wash the mattress or cushions in conventional washing machines.